1. Field of the Invention
The present invention relates to a liquid heating and circulating apparatus mounted in, for example, an electric car for heating and circulating liquid to heat a passenger compartment defined therein.
2. Description of Related Art
FIG. 2 depicts a conventional liquid heating and circulating apparatus mounted in an electric car. The liquid heating and circulating apparatus shown therein comprises a hot water generating unit 104 and an interior heat exchanger 105 connected to the hot water generating unit 104 via a plurality of pipes or tubes 106 so that a passenger compartment defined in the car may be heated by circulating the hot water. The hot water generating unit 104 comprises a main tank 102 having a heater 101 mounted therein for heating water contained therein, and a pump 103 juxtaposed with the main tank 102 for pumping and circulating hot water generated in the main tank 102. An auxiliary tank 107 is secured to the main tank 102 on an upper portion thereof so as to communicate therewith. The auxiliary tank 107 has a lid 107a mounted thereon through which water is supplemented to the hot water generating unit 104.
In the liquid heating and circulating apparatus of the above-described construction, however, the vapor pressure of the hot water circulating therein changes according to temperature changes of the hot water, resulting in a change in water level. Because of this, the main tank 102 is required to have the auxiliary tank 107 with the lid 107a directly mounted on the upper portion thereof, as described above. This construction has a problem in that the hot water generating unit 104 is restricted in its installation or layout.
The liquid heating and circulating apparatus is generally provided with a temperature switch (not shown) or the like for controlling the water temperature to a predetermined value. However, if such a water temperature control is out of order for some reason or other and the heater 101 is kept on, the hot water will boil and become vaporized and, hence, there is a good chance that the vaporized water may escape through the lid 107a and the auxiliary tank 107 may be emptied.